U.S. Pat. No. 4,474,281 discloses a coin validation apparatus wherein a pair of optical beams are directed across the coin path of a validator, substantially in the plane of a coin under test. The optical beams are spaced along the direction of travel of a coin in the coin path. The diameter of a coin is determined by timing the periods during which each of the optical beams is interrupted by passing coin, determining a value for the speed of the coin as it crosses the beams, deriving two diameter values from the timed periods and the speed values, and averaging the resultant values. The average produced is proportional to the diameter of the coin interrupting the beams.
If the apparatus of U.S. Pat. No. 4,474,281 is to function correctly, a coin to be tested must be in free fall before it encounters the first optical beam. A problem arises from this in that it is difficult to produce a compact validator with a sufficient run-in for a coin to be in free fall, before it interrupts the first optical beam. The problem is particularly acute in the case of validators for the large tokens used in some casinos.
DE-A-2 724 868 discloses an apparatus in which the diameter of a coin is checked on the basis of the time between the leading edge of the coin reaching a lower reference and the trailing edge of the coin leaving an upper reference position. However, this apparatus suffers from two disadvantages. Firstly, a counter is started when the coin reaches the upper reference position. Consequently, the upper reference position must be located at the diameter of the largest acceptable coin from the coin insertion slot. Secondly, the example, in which the diameter of a coin is checked on the basis of the time between the leading edge of the coin reaching a lower reference and the trailing edge of the coin leaving an upper reference position, cannot be used with coins whose diameters are not greater than the separation of the reference positions.
GB-A-1 405 936 discloses a coin validation apparatus comprising means defining first and second reference positions spaced along a coin path, sensor means for detecting a trading point on a coin passing the first reference position and a leading point on the coin reaching the second reference, and processing means for determining the velocity of a coin under test on the basis of the output of the sensor means. However, the diameter of the coin is checked using additional sensors.
In the following the term "coin" means coin, token and any similar objects representing value.